1. Field of the Invention
The present invention relates to a power-branched transmission having a plurality of transmission ratio ranges and a continuously variable transmission ratio.
2. Description of the Related Art
Automatic transmissions having a continuously variable transmission ratio are gaining in interest due to the higher driving comfort and convenience, and particularly because of lower fuel consumption as compared with conventional stepped automatic transmissions in motor vehicles that operate with planetary gear trains. Such continuously variable transmissions typically contain a variator, or variable speed drive, which is formed by two parallel pairs of spaced conical disks around which an endless torque-transmitting means passes, and wherein the spacing between the conical disks of the respective conical disk pairs is variable in opposite directions to change the transmission ratio.
One problem with such variable speed drives is their limited transmission ratio variation range and their limited torque transmitting capacity. In order to increase the transmission spread, i.e., the transmission ratio variation range and the torque transmitting capacity, power-branched automatic transmissions have been created, with which the variable speed drive is connected to a gear train via at least one clutch in various ways. The variation range of the variable speed drive is traversed depending on the clutch position, while changing the ratio of the transmission as a whole in one direction or the other, so that an enlarged overall transmission ratio spread results while the variable speed drive ratio spread remains the same or is even reduced. Furthermore, at least in a power-branched transmission in which part of the drive torque is transmitted parallel to the variable speed drive through the clutch directly to the gear train or the take-off, a variable speed drive does not have to transmit the entire drive torque, as a result of which the torque transmitting capacity of the transmission is increased.
Such power-branched continuously variable transmissions have also become known as hybrid machines, i.e., with an integrated electrical machine.
Power-branched, continuously variable transmissions, so-called CVT transmissions, that have a planetary gear train in addition to the variable speed drive are known from U.S. Pat. No. 3,340,749 and from DE 12 32 834. The planetary gear train is integrated into the transmission in such a way that it is positioned between the take-off and the variable speed drive. The drive of the transmission is connected to one of the variable speed drive shafts in a rotationally fixed connection, but none of the rotary shafts has a rotationally fixed connection to the take-off.
From published German applications DE 102 47 174 A1 and DE 103 58 114 A1 transmission structures with a variable speed drive and a planetary gear train are known in which the planetary gear set is installed in such a way that it is positioned between the variable speed drive and the drive engine. That means that none of the variable speed drive shafts has a rotationally fixed connection to the drive engine, but one of the variable speed drive shafts has a rotationally fixed connection to the take-off from the transmission. In particular, in those structures the drive engine is connected to the planet pinion carrier of the planetary gear train, and the planetary gear train is executed as a negative gear train. Those structures are therefore favorable in terms of uniform division of power, a fact that is attributable to the planet pinion carrier being connected to the transmission input. On the other hand, it is relatively complicated to implement a reverse gear, so that an additional shaft is usually necessary to reverse the direction of rotation at the output side.
Starting from that as a basis, an object of the present invention is to provide a power-branched transmission having a plurality of transmission ratio ranges with continuously variable transmission ratio, wherein the power division is matched to the utilization of the various transmission ratios in a passenger car transmission.
Those problems are solved with a power-branched transmission in accordance with the invention as herein described and claimed.